1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * ee1004 - driver for DDR4 SPD EEPROMs 4 * 5 * Copyright (C) 2017-2019 Jean Delvare 6 * 7 * Based on the at24 driver: 8 * Copyright (C) 2005-2007 David Brownell 9 * Copyright (C) 2008 Wolfram Sang, Pengutronix 10 */ 11 12 #include <linux/err.h> 13 #include <linux/i2c.h> 14 #include <linux/init.h> 15 #include <linux/kernel.h> 16 #include <linux/list.h> 17 #include <linux/mod_devicetable.h> 18 #include <linux/module.h> 19 #include <linux/mutex.h> 20 21 /* 22 * DDR4 memory modules use special EEPROMs following the Jedec EE1004 23 * specification. These are 512-byte EEPROMs using a single I2C address 24 * in the 0x50-0x57 range for data. One of two 256-byte page is selected 25 * by writing a command to I2C address 0x36 or 0x37 on the same I2C bus. 26 * 27 * Therefore we need to request these 2 additional addresses, and serialize 28 * access to all such EEPROMs with a single mutex. 29 * 30 * We assume it is safe to read up to 32 bytes at once from these EEPROMs. 31 * We use SMBus access even if I2C is available, these EEPROMs are small 32 * enough, and reading from them infrequent enough, that we favor simplicity 33 * over performance. 34 */ 35 36 #define EE1004_ADDR_SET_PAGE0 0x36 37 #define EE1004_ADDR_SET_PAGE1 0x37 38 #define EE1004_NUM_PAGES 2 39 #define EE1004_PAGE_SIZE 256 40 #define EE1004_PAGE_SHIFT 8 41 #define EE1004_EEPROM_SIZE (EE1004_PAGE_SIZE * EE1004_NUM_PAGES) 42 43 struct ee1004_bus { 44 struct kref kref; 45 struct list_head list; 46 struct mutex lock; 47 struct i2c_adapter *adapter; 48 struct i2c_client *set_page_clients[EE1004_NUM_PAGES]; 49 int page; 50 }; 51 52 static LIST_HEAD(ee1004_busses); 53 static DEFINE_MUTEX(ee1004_busses_lock); 54 55 static const struct i2c_device_id ee1004_ids[] = { 56 { "ee1004", 0 }, 57 { } 58 }; 59 MODULE_DEVICE_TABLE(i2c, ee1004_ids); 60 61 /*-------------------------------------------------------------------------*/ 62 63 static int ee1004_get_current_page(struct ee1004_bus *bus) 64 { 65 int err; 66 67 err = i2c_smbus_read_byte(bus->set_page_clients[0]); 68 if (err == -ENXIO) { 69 /* Nack means page 1 is selected */ 70 return 1; 71 } 72 if (err < 0) { 73 /* Anything else is a real error, bail out */ 74 return err; 75 } 76 77 /* Ack means page 0 is selected, returned value meaningless */ 78 return 0; 79 } 80 81 static int ee1004_set_current_page(struct ee1004_bus *bus, int page) 82 { 83 int ret; 84 85 if (page == bus->page) 86 return 0; 87 88 /* Data is ignored */ 89 ret = i2c_smbus_write_byte(bus->set_page_clients[page], 0x00); 90 91 /* 92 * Don't give up just yet. Some memory modules will select the page 93 * but not ack the command. Check which page is selected now. 94 */ 95 if (ret == -ENXIO && ee1004_get_current_page(bus) == page) 96 ret = 0; 97 if (ret < 0) 98 return ret; 99 100 bus->page = page; 101 return 0; 102 } 103 104 static ssize_t ee1004_eeprom_read(struct i2c_client *client, struct ee1004_bus *bus, char *buf, 105 unsigned int offset, size_t count) 106 { 107 int status, page; 108 109 page = offset >> EE1004_PAGE_SHIFT; 110 offset &= (1 << EE1004_PAGE_SHIFT) - 1; 111 112 status = ee1004_set_current_page(bus, page); 113 if (status) { 114 dev_err(&client->dev, "Failed to select page %d (%d)\n", page, status); 115 return status; 116 } 117 118 /* Can't cross page boundaries */ 119 if (offset + count > EE1004_PAGE_SIZE) 120 count = EE1004_PAGE_SIZE - offset; 121 122 if (count > I2C_SMBUS_BLOCK_MAX) 123 count = I2C_SMBUS_BLOCK_MAX; 124 125 return i2c_smbus_read_i2c_block_data_or_emulated(client, offset, count, buf); 126 } 127 128 static ssize_t eeprom_read(struct file *filp, struct kobject *kobj, 129 struct bin_attribute *bin_attr, 130 char *buf, loff_t off, size_t count) 131 { 132 struct i2c_client *client = kobj_to_i2c_client(kobj); 133 struct ee1004_bus *bus = i2c_get_clientdata(client); 134 size_t requested = count; 135 int ret = 0; 136 137 /* 138 * Read data from chip, protecting against concurrent access to 139 * other EE1004 SPD EEPROMs on the same adapter. 140 */ 141 mutex_lock(&bus->lock); 142 143 while (count) { 144 ret = ee1004_eeprom_read(client, bus, buf, off, count); 145 if (ret < 0) 146 goto out; 147 148 buf += ret; 149 off += ret; 150 count -= ret; 151 } 152 out: 153 mutex_unlock(&bus->lock); 154 155 return ret < 0 ? ret : requested; 156 } 157 158 static BIN_ATTR_RO(eeprom, EE1004_EEPROM_SIZE); 159 160 static struct bin_attribute *ee1004_attrs[] = { 161 &bin_attr_eeprom, 162 NULL 163 }; 164 165 BIN_ATTRIBUTE_GROUPS(ee1004); 166 167 static void ee1004_bus_unregister(struct ee1004_bus *bus) 168 { 169 i2c_unregister_device(bus->set_page_clients[1]); 170 i2c_unregister_device(bus->set_page_clients[0]); 171 } 172 173 static void ee1004_bus_release(struct kref *kref) 174 { 175 struct ee1004_bus *bus = container_of(kref, struct ee1004_bus, kref); 176 177 ee1004_bus_unregister(bus); 178 179 mutex_lock(&ee1004_busses_lock); 180 list_del(&bus->list); 181 mutex_unlock(&ee1004_busses_lock); 182 183 kfree(bus); 184 } 185 186 static int ee1004_bus_initialize(struct ee1004_bus *bus, struct i2c_adapter *adapter) 187 { 188 bus->set_page_clients[0] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE0); 189 if (IS_ERR(bus->set_page_clients[0])) 190 return PTR_ERR(bus->set_page_clients[0]); 191 192 bus->set_page_clients[1] = i2c_new_dummy_device(adapter, EE1004_ADDR_SET_PAGE1); 193 if (IS_ERR(bus->set_page_clients[1])) { 194 i2c_unregister_device(bus->set_page_clients[0]); 195 return PTR_ERR(bus->set_page_clients[1]); 196 } 197 198 bus->page = ee1004_get_current_page(bus); 199 if (bus->page < 0) { 200 ee1004_bus_unregister(bus); 201 return bus->page; 202 } 203 204 kref_init(&bus->kref); 205 list_add(&bus->list, &ee1004_busses); 206 mutex_init(&bus->lock); 207 bus->adapter = adapter; 208 209 return 0; 210 } 211 212 static int ee1004_probe(struct i2c_client *client) 213 { 214 struct ee1004_bus *bus; 215 bool found = false; 216 int rc = 0; 217 218 /* Make sure we can operate on this adapter */ 219 if (!i2c_check_functionality(client->adapter, 220 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_I2C_BLOCK) && 221 !i2c_check_functionality(client->adapter, 222 I2C_FUNC_SMBUS_BYTE | I2C_FUNC_SMBUS_READ_BYTE_DATA)) 223 return -EPFNOSUPPORT; 224 225 mutex_lock(&ee1004_busses_lock); 226 list_for_each_entry(bus, &ee1004_busses, list) { 227 if (bus->adapter == client->adapter) { 228 kref_get(&bus->kref); 229 found = true; 230 break; 231 } 232 } 233 234 if (!found) { 235 bus = kzalloc(sizeof(*bus), GFP_KERNEL); 236 if (!bus) { 237 rc = -ENOMEM; 238 goto unlock; 239 } 240 241 rc = ee1004_bus_initialize(bus, client->adapter); 242 if (rc) { 243 kfree(bus); 244 goto unlock; 245 } 246 } 247 248 i2c_set_clientdata(client, bus); 249 250 dev_info(&client->dev, 251 "%u byte EE1004-compliant SPD EEPROM, read-only\n", 252 EE1004_EEPROM_SIZE); 253 254 unlock: 255 mutex_unlock(&ee1004_busses_lock); 256 return rc; 257 } 258 259 static void ee1004_remove(struct i2c_client *client) 260 { 261 struct ee1004_bus *bus = i2c_get_clientdata(client); 262 263 kref_put(&bus->kref, ee1004_bus_release); 264 } 265 266 /*-------------------------------------------------------------------------*/ 267 268 static struct i2c_driver ee1004_driver = { 269 .driver = { 270 .name = "ee1004", 271 .dev_groups = ee1004_groups, 272 }, 273 .probe = ee1004_probe, 274 .remove = ee1004_remove, 275 .id_table = ee1004_ids, 276 }; 277 module_i2c_driver(ee1004_driver); 278 279 MODULE_DESCRIPTION("Driver for EE1004-compliant DDR4 SPD EEPROMs"); 280 MODULE_AUTHOR("Jean Delvare"); 281 MODULE_LICENSE("GPL"); 282